DESCRIPTION Traumatic brain injury (TBI) is a major source of disability among military and civilian populations. Unfortunately, the pathophysiology of the motor, cognitive, and affective dysfunction that can result from TBI remains incompletely understood. In right handed people with typical brain organization, the left hemisphere is dominant for the praxis systems that mediate how (postural and spatial-temporal movement parameters) we perform skilled purposeful movements, and the right hemisphere mediates action-intention systems that determine when we start, continue, stop, and inhibit our actions. Each hemisphere also controls movements of the limbs on the opposite side of the body. The corpus callosum is the major white matter structure that transmits information between the two cerebral hemispheres, and it is particularly susceptible to damage from TBI (Rubens et al, 1977), including mild TBI (Inglese et al, 2005; Wilde et al, 2008). Damage to the corpus callosum can impair the interhemispheric communication necessary for bimanual coordination, isolate the left hemisphere praxis systems from the right hemisphere (which controls the left hand), and isolate the right hemisphere action-intention systems from the left hemisphere (which controls the right hand). The purpose of this study is to test the hypothesis that specific and dissociable types of motor dysfunction result from traumatic injury to the left hemisphere, the right hemisphere, and the corpus callosum. For this proposed study, we will recruit approximately 16 experimental participants with moderate to severe TBI from closed head trauma, 16 with mild TBI from closed head trauma, and 16 matched controls who have not sustained TBI. This sample size was determined based on feasibility of recruitment within the two year time period of the CDA1 program. Data from this study will then be used for a power analysis to determine the sample size necessary for continuation of this project for future research including application to the CDA2 program. The AIMS of this study are to utilize behavioral-motor tasks to 1) test the hypothesis that people with TBI will have motor impairments resultant from dysfunction of the left hemisphere praxis systems (impaired production of gestures and deft fine finger movements) and right hemisphere action intention systems (motor impersistence and impairments of reaction times and motor response inhibition), and that in some people with a history of TBI, there will be a double dissociation of these types of impairments thus demonstrating that TBI can lead to selective impairments of these two systems; 2) test the hypothesis that people with TBI will have motor impairments attributable to callosal disconnection: apraxic deficits greater in the left hand than the right, action-intention deficits greater in the right hand than the left, and impaired bimanual in-phase and antiphase movements; 3) correlate the presence of motor impairments due to damage to praxis systems, action-intention systems, and callosal disconnection with impairments in daily functional ability as measured by the Disability of Arm Shoulder and Hand (DASH) scale. A characterization of distinct types of motor dysfunction that result from TBI is essential to understand the pathophysiology of TBI and the nature of the motor disability, to monitor recovery, and to guide individualized rehabilitation strategies that will be a focus of future research. PUBLIC HEALTH RELEVANCE: The Department of Defense reports 233,425 cases of TBI among service members of the US military from 2000-2011, with at least 94% of these cases caused by closed head injuries (Defense and Veterans Brain Injury Center website, 2012). Motor impairments are common after TBI, and their presence correlates with both functional disability and performance on other neuropsychological measures (Clifton et al, 1993). The nature of these motor impairments is not fully understood. This study aims to demonstrate the pathophysiological basis for distinct types of motor impairments that result from closed head trauma and to correlate these different types of motor impairments with functional disability. This research will add to our knowledge of the disability and prognosis after TBI and has the potential to lead to individualized rehabilitative interventions through future research.